You're right it's very rare to see anyone wearing a helmet whilst scrambling in the UK, that doesn't mean it's not a good idea though! As with a lot of safety equipment, it comes down to personal risk perception.

One thing worth bearing in mind is how busy the route is. The popular routes in the UK will often have a lot of inexperienced scramblers on them, who might be less careful than you at not dislodging loose rocks. Countering this argument is that the popular routes have often had a lot of the loose stuff knocked off already!

Personally I would - unless perhaps you definitely know that for the particular area and route you're taking the risk is minimal. Just because others may not be as cautious doesn't necessarily make it ok!

Yes, there are practical disadvantages with carrying the thing and having to wear it, but it only takes one loose rock to strike you on the head to seriously injure you.

Everything is a tradeoff, so never does any harm is just plain wrong. The "harm" in this case includes extra bulk and weight to carry, additional fatigued caused by that, less enjoyment due to shlepping the helmet and possibly wearing it if you don't like helmets, etc. The real question is whether those "harms" are worth it, which I'm not addressing. My point is that knee jerk "always do ..." answers without any discussion of the downside are wrong or misleading at best, this one being no exception.
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Olin LathropDec 11 '12 at 16:21

@OlinLathrop You make a good point, though I think your analysis is rather strong (I think it's fair to assume that by "harm" I was excluding the more obvious practical considerations such as wearing it and carrying it - I wouldn't feel compelled to discuss the downsides of carrying a map or compass in the wilderness if someone asked for instance!)
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berry120Dec 11 '12 at 16:32